Unprecedented; extraordinary and unmatched in prior experience — often used in formal or news contexts (e.g., large-scale disasters).
未曾有の大地震で町は壊滅的な被害を受けた。
The town suffered devastating damage from an unprecedented earthquake.
その企業は未曾有の業績悪化に直面している。
The company is facing an unprecedented decline in performance.
未曾有という言葉が報道で多用されるほどの大事件だった。
It was such a major incident that the word 'unprecedented' was used frequently in reports.